The invention relates to a disc brake, in particular for a commercial vehicle, having functional components which can be reused after use and subsequent examination for operational safety.
It is known to reuse, that is to say again install in a commercial vehicle, disc brakes which have been removed within the scope of maintenance work, i.e. removed from the commercial vehicle after inspection of the functional components and, if appropriate, their replacement or refurbishment.
Reusing functional components of the disc brake permits the high material value and fabrication expenditure of the components to be largely utilized, which provides a cost-effective alternative to newly fabricated functional components.
However, the use of such used functional components is problematic insofar as it has hitherto not been possible to detect whether the respective functional component in its further use will sufficiently withstand the operational loading over a predefined service life. That is to say, the functioning and reliability of the refurbished disc brake must not be adversely affected by possible deficiencies of the reused components.
In fact, given a series of functional components of the disc brake, it is not possible to detect what stresses this functional component, for example the brake caliper, was subjected to until its removal.
Moreover, many functional components are configured according to fatigue strength criteria, which results in a service life of a defined limited length.
In particular, as mentioned, for reasons of economy but also in order to save resources, there is a requirement to use the maximum functional components of a used brake for a reworked product. For this purpose, a high level of reliability of the evaluation of the components is necessary, not least for reasons of guarantee and product liability.
It is known to reuse assemblies from other fields in the prior art, said reuse usually being preceded by the following steps:                return and collection of used, discarded functional components,        if appropriate separating out of unsuitable functional components (e.g. heavily damaged ones),        identification of the type of equipment and version,        cleaning of the assembly,        removal of the functional components,        cleaning and inspection of the functional components,        if appropriate classification according to defined criteria (e.g. wear limits),        if appropriate reworking of functional components,        mounting of equipment with reused (if appropriate reworked) and, where necessary, new components,        functional checking, and characterization as a reworked product.        
The step “selection of reusable functional components”, which requires reliable assessment with respect to the remaining service life of the functional component which can be expected, is critical here.
This assessment is made according to various criteria such as damage, deformation, corrosion and wear, which are examined visually or with aids (e.g. measurement, X-rays, fracture detection, etc.). This permits the functional components with clear damage to be identified and separated out.
Alternatively, if possible, these functional components can be fed to means for reworking, e.g. by way of mechanical subsequent machining, surface treatment or the like, and subsequently reused.
In contrast, it is not possible to determine or estimate the remaining usable service life of such functional components which do not exhibit any of the abovementioned detectable features.
Whereas, owing to safety considerations, it is obvious to exchange low-value components for a new component instead of reusing them, this constitutes a decisive economic problem for components which involve a high expenditure of material or fabrication expenditure.
The brake caliper of a disc brake, for example, forms such a large proportion of the total manufacturing costs of the disc brake that replacement by a new part would make reworking the respective disc brake uneconomic overall.
The described customary method for selecting reusable functional components is based essentially on empirical values. Used components without obvious damage features can be reused in this context without there being reliable decision criteria for their remaining service life, which can result in risks for the user and manufacturer. In particular, such a procedure is not acceptable for safety-relevant functional components.
Similarly, the use of a modified technical specification for reworked assemblies, which specification permits a reduced service life compared to a new assembly, does not entail the abovementioned problems. The functioning of a used functional component with an unknown remaining service life likewise cannot be ensured for such restricted requirements.
The results of product-accompanying trials with individual reworked disc brakes according to a reduced specification likewise do not permit conclusions to be drawn about the remaining service lives of other reworked brakes, since the remaining service life for each of the disc brakes in question is specific and can vary greatly depending on the state of the used components.
In order to estimate the utilization rate of the fatigue strength of, for example, a brake caliper, generally loading-relevant values are required and stored separately. However, this is possible only with considerable financial outlay and, moreover, constitutes a solution which is susceptible to faults.
The invention is based on the object of developing a disc brake of the generic type in such a way that reusability after use becomes reliably possible, in particular with respect to safety-relevant functional components.
Accordingly, at least the safety-relevant functional components are each equipped with an indicator which is distinguished, in terms of the loading, by a service life which is shorter, for operational reasons, than the safety-relevant ranges of the respective functional component.
In this context, this indicator is embodied in such a way that detectable damage occurs if the remaining service life of the functional component is not sufficient in order to permit reuse with the necessary operational safety.
Safety-relevant functional components which are provided with such an indicator are considered to be, for example, the brake caliper, a brake lever or a bridge. When braking occurs, the bridge is pressed by way of the brake lever against a brake pad which is in turn pressed against a vehicle-side brake disc.
The brake lever can be pivoted by use of roller bearings which are supported on the bridge or on the brake caliper.
According to a further aspect of the invention, the indicator can be embodied as a fin or web, wherein a plurality of such fins can be provided on the respective functional components.
The brake lever, like the brake caliper and the bridge, is usually manufactured as a cast part, with the result that it is appropriate here to integrally form the indicator thereon. However, it is also contemplated to carry out processing of the functional components in order to form the indicator.
The dimensioning of the indicator, in the sense that it is damaged, i.e. deformed or destroyed, when a predetermined loading limit is reached, takes place in advance on the basis of the available data for the functional component, the service life of which is already predefined on the basis of various loading parameters.
The indicator, as an example the specified fin, can certainly also be implemented with a different design. In this respect, a spring element, clamped-in wire or the like or a piece of sheet metal which is integrally cast in or connected in a positively locking fashion are possible.
Furthermore, DU bearings, with embedded contacts, which interrupt, for example, a potential signal given corresponding wear, can serve as indicators.
The abovementioned roller bearings, usually needle bearings, which pivotably support the brake lever are embodied in such a way that a needle is provided with at least one notch or a reduced length as an indicator.
Widening of the brake caliper, such as typically occurs, can be tapped by way of a pad retaining clip, which spans the mounting opening of the brake caliper, and determined in this way.
In any case, it is ensured that only functional components, and as a result only a disc brake, which correspond to the safety-relevant requirements, are re-used.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.